In motor vehicles today, the internal combustion engine is started by a conventional starter. This starter and its connection to the crankshaft are implemented so that the starting torque required for starting the engine is applicable at any time, even at extremely low temperatures (less than −10° C.). The electric current required for this is usually supplied by a 12-volt lead-acid battery.
Motor vehicles having a hybrid drive, as described in PCT International Patent Application No. DE99/03026 and in German Patent Application No. 197 39 906, have one or more electric machines, which may be operated either as motors or as generators, in addition to the internal combustion engine.
A conventional starter is usually omitted in such a hybrid drive. Electric machines in the vehicle assume the function of starter. Since the connection of the electric machines to the internal combustion engine is not optimized for starting the engine, these electric machines require a high electric current from the battery. Although the battery of a hybrid vehicle is designed for a much higher power level than the battery in a conventional vehicle, batteries are frequently unable to meet the electric power demand at cold temperatures in particular.